sdu faculty of forestry journal special edition 2009 - Orman Fakültesi

SDU Faculty of Forestry Journal
Serial: A, Number: Special Issue, Year: 2009, ISSN: 1302-7085, Page: 243-244
THREATENING TREE DISEASE IN EAST AFRICA
Pia BARKLUND 1* , Jane NJUGUNA 1,2 , Abdella GURE 3 , Philip NYEKO 4 ,
Katarina IHRMARK 1 and Jan STENLID 1
1 Department of Forest Mycology and Pathology SLU, Box 7026,75007 Uppsala Sweden.
2 Kenya Forest Research Institute, P.O. Box 20412 Nairobi City Square 00200, Kenya.
3 Wondo Genet College of Forestry and Natural Resources, Hawassa University, P.O. Box 128
Shashemane Ethiopia
4 Department of Forest Biology and Ecosystems Management, Makerere University,P.O Box
7062, Kampala, Uganda.
ABSTRACT
*pia.barklund@mykopat.slu.se
Severe and extensive outbreaks of a dieback and canker disease have recently
been observed on Grevillea robusta in Kenya, Uganda and to a lesser extent in
Ethiopia. Grevillea is an excellent agroforestry tree species grown intensively in
east Africa to improve agricultural land use and rural livelihoods, and provide food
security. Our recent studies on the disease indicate that 50-80% tree mortality
occurs on severely infected farms. It is caused by Botryosphaeria spp., a fungal
genus containing many species and more than one pathogenic species can occur in
diseased trees. Samples were taken from Grevillea trees growing in different
agroecological zones and from some other tree species with similar symptoms.
Morphological and molecular methods were used to identify species and to study
differences between populations in different agroecological zones as well as
countries.
The disease is more severe in dry areas than wet ones, emphasizing the need
for proper species-site matching. Several other tree species, including indigenous
and exotics, were found infected by Botryosphaeria in the region. Especially
alarming is the attack on different Eucalyptus species.
Such disease outbreaks may be attributed to increased tree planting in
agroforestry and commercial tree plantations in the region. Increased acreage and
number of trees/ha leads to an enlarged number of potential hosts, and a larger
population size for pathogens to evolve genetically into more aggressive
genotypes. Moreover, complex threats can arise when previously isolated fungal
species brought together by human interference hybridize posing threats to tree
hosts previously immune from their effects. Implications of the dieback and canker
disease on the scaling up of agroforestry technologies and commercial forestry in
the region are discussed.
Kewords: Grevillea robusta, Eucalyptus spp. Botryosphaeria, dieback and
canker disease
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